We are presented with 371 and 638. Let's work out the sum.

Step 1: We'll start by adding the digits 1 & 8 in column 1 and get 9.

Step 2: We'll start by adding the digits 7 & 3 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 3 & 6 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 371 + 638 = 1009.

